[SciPy-User] Populating a recarray from 0 size
Benjamin Root
ben.root@ou....
Sun Aug 22 14:13:36 CDT 2010
On Sun, Aug 22, 2010 at 1:46 PM, Joe Kington <jkington@wisc.edu> wrote:
>
>
> On Sun, Aug 22, 2010 at 12:44 PM, Benjamin Root <ben.root@ou.edu> wrote:
>
>> On Sat, Aug 21, 2010 at 8:18 PM, Sergi Pons Freixes <spons@utm.csic.es>wrote:
>>
>>> Hi everybody,
>>>
>>> I'm interested in populating a recarray a row at a time. I thought in
>>> using:
>>>
>>> -------
>>> # Creation of empty recarray
>>> names = ["cruise", "SEQ", "param", "r2", "stderr", "slope", "intercept"
>>> formats = ["i4", "i4", "S10", "f4", "f4", "f4", "f4"]
>>> statsc = scipy.empty(0, dtype={"names":names, "formats":formats})
>>>
>>> # Adding row and setting values
>>> statsc = scipy.resize(statsc, statsc.size + 1)
>>> statsc["cruise"][-1] = cr
>>> statsc["SEQ"][-1] = ca
>>> statsc["param"][-1] = yvar
>>> ...
>>> -------
>>>
>>> But scipy.resize complains with:
>>> statsc = scipy.resize(statsc, statsc.size + 1)
>>> File "/usr/lib/python2.6/site-packages/numpy/core/fromnumeric.py",
>>> line 833, in resize
>>> if not Na: return mu.zeros(new_shape, a.dtype.char)
>>> ValueError: Empty data-type
>>>
>>> So, is scipy not happy because statsc.size is 0 on the first resize?
>>> In this case, how could I overcome this limitation?
>>>
>>> Regards,
>>> Sergi
>>>
>>>
>> Sergi,
>>
>> I had a similar need recently. I was populating recarrays where I didn't
>> know the final size beforehand. The way I solved the problem was to create
>> an iterator function and use .fromiter() to build the array.
>>
>> A simplified example:
>>
>> import numpy
>>
>> class foobar(object) :
>> def __init__(self) :
>> self._myval = 0
>>
>> def __iter__(self) :
>> return self
>>
>> def next(self) :
>> if self._myval >= 7 :
>> raise StopIteration
>>
>> self._myval += 1
>> return self._myval
>>
>> gen = foobar()
>> a = numpy.fromiter(gen, dtype=[('Column', 'i4')])
>> print a
>>
>>
>> However... for some reason, I can't seem to get this working. Maybe
>> someone else can spot my error?
>>
>
> I think the iterator needs to return a tuple, rather than a "bare" int. At
> any rate, if you change "return self._myval" to "return (self._myval,)",
> things work perfectly.
>
Ah, right!
An even easier example would be:
def foobar(start, end) :
curVal = start
while curVal < end :
yield (curVal,)
curVal += 1
gen = foo(1, 10)
a = numpy.fromiter(gen, [('Column', 'i4')])
print a['Column']
Which woulld output:
[1 2 3 4 5 6 7 8 9]
I hope that helps!
Ben Root
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.scipy.org/pipermail/scipy-user/attachments/20100822/08982e79/attachment-0001.html
More information about the SciPy-User
mailing list